Fuel quality plays a significant role in the operation of an internal combustion engine. In auto-igniting internal combustion engines the quality of the fuel is critically important for the ignition of the fuel. For diesel fuels, therefore, the cetane number is usually specified, this number being a measure for how fast the fuel combusts in a diesel-powered internal combustion engine. In auto-igniting internal combustion engines the fuel is ignited by means of the compression heat. In addition to other parameters, such as compression level, crankshaft angle and fuel quantity, the cetane number in particular also influences the ignition quality following an injection. An auto-igniting internal combustion engine which is operated with fuel having a comparatively low cetane number is reluctant to start, runs more roughly and louder, and has poorer exhaust gas emission values. Fuels having a higher cetane number lead to faster ignition than fuels having a lower cetane number.
Since the cetane number therefore has an effect on the operating characteristics and in particular on the exhaust gas properties of an internal combustion engine, it is becoming an increasingly common practice to provide fuel quality sensors in the fuel supply tract of an internal combustion engine in order to measure the fuel quality. Even a deviation from a nominal fuel quality due to time-related and/or regional factors can then remain without undesirable consequences for the operation of the internal combustion engine.